The CSP has a structure in which a plurality of electrode pads are formed on one surface of a silicon (Si) substrate in which a plurality of semiconductor devices such as transistors (not illustrated) are provided, and each of the plurality of electrode pads is connected with a different bump as an external terminal (see, for example, Patent Literature 1).
FIG. 12A is a partial cross-sectional view of the CSP at one bump.
As shown in FIG. 12A, on one surface of a Si substrate 200, an electrode pad 202 is formed. Also, a protection film 204 made of silicone nitride (Si3N4) is formed to cover a circumferential edge portion of the electrode pad 202 and the surface of the substrate except for the area under the electrode pad 202. A metal layer 206 made of Under Barrier Metal (UBM) is formed to cover an exposed portion of the surface of the electrode pad 202 and a portion of the protection film 204 surrounding an opening on the exposed portion. The metal layer 206 is connected with a bump 208.
The connection of the bump 208 with the metal layer 206 is performed, for example, as follows.
That is to say, the bump is connected with the metal layer by first applying flux to the surface of the metal layer, then putting, as a bump material, a solder ball made of, for example, a Sn—Ag-based lead-free solder material onto the flux-applied surface, and melting part of the solder ball by the reflow.